Magnetic switch



Sept l2, 1961 R. E. sTANAwAY 2,999,914

MAGNETIC SWITCH Filed Dec. 23, 1957 United States Patent() 2,999,914MAGNETIC SWITCH Robert Edward Stanaway, Pasadena, Calif., assgnor, bymesne assignments, to Consolidated Electrodynamics Corporation,Pasadena, Calif., a corporation of Callfornia Filed Dec. 23, 1957, Ser.No. 704,557 5 Claims. (Cl. 200-`87) This invention relates to mechanicalswitches and more particularly to such switches which may bemagnetically controlled.

In the field of switch devices it is desirable to obtain a switch whichcan be opened and closed at a high rate, yet with a minimum of contactnoise so that low level signals on the order of several microamps can beswitched. Where a large number of electrical devices are to beinterrogated at high speeds, it is customary in many instances to employa commutating switch of the type having a plurality of stationarycontacts and a moving arm. -The various devices interrogated have anoutput signal level connected to the various stationary contacts of thecommutating switch. The movable arm is rotated, and once each revolutionit engages the stationary contacts, thereby interrogating the variousdevices once each revolution. The wiping action of the moving contact asits crosses the stationary contacts presents several disadvantages,among which are substantially large electrical noise signals from thewiping action and a relatively short useful life from the frictionalengagement of the wiping contact with the stationary contacts. As aconsequence, electrical output signals having an amplitude lower thanthat of the electrical contact noise -cannot be detected, and because ofthe frictional wear and tear of the stationary contacts and the wipingcontact, the useful life of such a commutating switch is limited, andthe necessity for periodic repair or replacement renders such aswitching device expensive to use as well as often unreliable after onlya few hours of use.

In order to overcome the foregoing disadvantage a Switch is providedaccording to the present invention which is magnetically operated andcontrolled, and a plurality of them may be employed as a commutatingswitch which has no wiping contacts. High speed sampling of low levelsignals is permissible, and such switch is simple and easy tomanufacture. Furthermore, it has a long useful life, is relativelysmall, and is inexpensive to manufacture and maintain.

According to the present invention, any leaf-type switch may be employedprovided the leaves are magnetizable. Numerous magnetic relays,commercially available, may be suitable. A small magnet such as a barmagnet is :fixed in position within a critical zone. The critical zonecan be ascertained my moving -the magnet toward the switch until thecontacts close and withdrawing the magnet until the contacts open. Theposition where the magnet causes the relay contacts to close can bedefined as one boundary of the critical zone. The position where thecontacts open can be defined as another boundary of the critical zone.If the magnet is iixed in position in the critical zone between the twoboundaries thus ascertained, but not on these boundaries, a magneticl'field is supplied to the switch which serves to maintain the switchcontacts in whatever position they occupy. For example, if the contactsare closed, they are maintained closed; whereas, if the contacts areopen, they are maintained in the open position.

Another magnet is brought into the vicinity of the xed magnet with itspoles arranged to aid the magnetic field of the fixed magnet and of suchmagnetic iield strength that the resulting magnetic iield applied to theleaf-type 2,999,914 Patented Sept. 12, 1961 switch is sutiicientlystrong to polarize the leaf members and close them by magneticattraction. If the contacts are open beforehand, they are closed by thisoperation. If, on the other hand, they are closed beforehand, thisoperation is uneventful. At any rate, the leaf members and associatedcontacts are closed after this operation. Since the fixed magnet locatedin the critical zone is capable of maintaining the contacts in whateverposition they occupy, it is seen that the contacts remain closed whenthe movable magnet is moved from the vicinity of the fixed magnet.

When it is desired to open the relay contacts, a magnet having polesthat oppose the fixed magnet is brought into the vicinity of the fixedmagnet. This movable magnet may be the same one used in the closingoperation. If so, it must be rotated to reverse'the position of thepoles. On the other hand, the movable magnet may be an additional magnetwhich has its poles reversed with respect to the closing magnet. In anyevent, the Imagnetic field of the opening magnet opposes the magneticfield of the magnet fixed in located in the critical zone. Consequently,the resulting magnetic iield applied to the arms of the contacts isrendered so small that the magnetic force attracting the leaf members isless than the spring force tending to separate them, and the leafmembers separate. Since -the fixed magnet within the critical zoneserves to maintain the contacts in whatever position they occupy, it isseen that the contacts remain open when the movable magnet is withdrawnfrom the vicinity of the fixed magnet.

By this novel arrangement a switch is provided which may employ a ixedmagnet located in a critical zone and two movable magnets oppositelypoled. By providing for movement of the movable magnets to and away fromthe vicinity of a xed magnet, the switch may be closed, then opened.Alternatively, by reversing the poles of each magnet, the switch may :beopened, then closed. In each instance, however, the switch is bi-stablein its operation because ythe fixed magnet in the critical zone servesto maintain the leaf-type contact arms in whatever position they occupywhenever a movable magnet is brought inot the vicinity thereof andremoved.

A commutating switch device without wiping contacts may be providedaccording to this invention by arranging a plurality of such switches ina given pattern, arranging fixed magnets in a critical zone with respectto the switches, and providing for a pair of movable anms on which aremounted magnets of oppositely disposed poles. By controlling the speedof the movable arms, the switches can be operated at a desired ratewithout the use of wiping contacts. Electrical noise signals from wipingcontacts is eliminated and a commutati-ng device having an extremelylong and useful life is provided.

Whenever moving magnets lare employed in or near closed electricalcircuits, the problem of induced signals arises, and in order to secureaccurate measurements of electrical signals from devices underinterrogation, it is necessary to eliminate the effects of the inducedsignals. The problem associated with induced signals is overcome in thepresent invention by displacing the movable arms on which the magnets ofoppositely disposed poles are mounted. I-f the displacement of themovable magnets is sufliciently great, a region therebetween can besecured which is substantially free of 4any magnetic field. The size ofsuch a region may be varied by changing the strength of the magnetsemployed as well as their displacement from one another. The time duringwhich such a field free region is present `at a given switch isdetermined by the speed of the movable magnets. Such factors as polestrength, displacement of the magnets and speed of the magnets can bevaried to provide a given period during which no signals are induced ineach of the plurality of magnetic switches and the associated`electrical circuits under interrogation. It is during this period thatthe electrical devices under interrogation Vare sampled and an accuratemeasurement made of their electrical output signals, substantially freeand clear of any induced signal from the movable magnets which servetoopen and close the various circuits in a given order. Accurateelectrical measurements can be made with a commutating device of thistype operated at high speed.

These and other features of this invention may be more fully appreciatedwhen considered in the light of the following specification and drawingsin which:

FIG. l illustrates the invention in its most elementa form.

FIGS. 2 and 3 illustrate the invention employed in a commutating switchdevice.

Referring first to FIG. l, the present invention is described first withreference to a single switch. Within a glass envelope a pair of switchcontacts 12 and 14 are `disposed on respective exible arms 16 and 18which in `turn are connected to respective terminals 20 and 22. Theflexible arms resist movement, vand when closed, they exert a springforce which tends to separate them. Where this force is less than thatdesired, small bias springs may be used on one or both of the arms 16and 18 to separate the contacts 12 and 14.

If a magnet 24 of given eld strength is disposed as shown at a distanceX from the switch arm 18, the magnetic field applied to the switch arms16 and 18 is sufficiently strong to polarize these arms and cause them-to close against the spring tension which normally holds apart thecontacts 12 and 14. If the magnet 24 is moved away from the switch adistance Y as indicated in the dotted line position, the magnetic fieldapplied to the switch arms 16 and 18 is diminished to the point Wherethe polarized arms have a force of magnetic attraction which is lessthan the mechanical spring bias force tending to separate the contacts.Consequently the spring bias forces the contacts apart and the switch isopened. The region between the X and Y locations may be referred to asthe critical zone, and if the magnet 24 is fixed in position within thiszone, it serves to hold the contacts 12 and 14 in whatever position theyoccupy, either closed or open. It is pointed out that the magnet 24cannot occupy either of the two positions shown. If the magnet is placeda distance X from the switch, the switch always remains closed, and ifthe magnet is placed at a distance Y from the switch, the switch isnever held closed. Therefore, the magnet 24 must lie somewhere betweenthe two positions shown. Assuming the contacts 12 and 14 are closed, themagnetic field from the magnet 24, tending to hold these contactsclosed, approaches a maximum as the position of the magnet 24 approachesthe distance X from the switch, and this magnetic force approaches `arhinimum as the magnet 24 approaches the distance Y from the switch.This assumes of course that the magnet 24 always remains within thatcritical zone defined by the X or Y positions indicated and does notoccupy either the X or Y position.

There are numerous other regions within which a critical zone isdelineated. If the center of the magnet 24 is shifted to the right orleft to respective dotted lines 27 and 28, a closure of the blades 16and 18 is effected if the magnet 24 is moved to the upper extremity ofeither line and a release of the blades is effected if the magnet ismoved to the lower extremity of the same line. Other lines parallel tothe lines 26, 27 and 28 and located at intermediate positions likewisedefine critical zones. Still other critical zones may be determined bymoving the magnet 24 to the right and left but parallel with thelongitudinal axis of the blades 16 and 18. To simplify the illustration,another magnet 29 is employed, Positioned as shown, the magnet 29effects a closure of the blades 16 `and 18. If moved right to the dottedline position 4 indicated, theimagnet 29 permits a release of theblades. Thus a critical zone is defined intermediate these twopositions. If the magnet 29 is moved within la correspending area on theleft end of the envelope 10, another critical zone is defined.l If themagnet 29 is moved from the position shown in FIG. l toward the envelope1li` and to the right still further critical zones can be determined. Ifthe magnet 29 is moved left from the position indicated and away fromthe envelope 10, still other critical zones are found. When a criticalzone is definedby placing the center of the magnet opposite the centerof the envelope 1f), the magnet is at the greatest lateral distance fromthe switch for critical zones involving movement of the magnet 24longitudinally and parallel with the axis of the switch.

From the foregoing discussion it is seen that numerous regionsconstitute critical zones. A magnet placed within such zone serves toprovide a field which magnetizes the switch arms and holds them closedonce they are closed by any other means and permits the switch arms tore- -rnain open if they are opened by any other means.

Stated in the alternative, the magnet in a critical zone supplies amagnetic field to the switch blades which is effective to maintain theblades in whatever position they occupy, either the opened or closedposition.

If the magnet 24 is fixed in position somewhere within a determinedcritical zone and if the contacts 12 and 14 are pressed together by somemeans not shown, the magnetic field from the magnet 24 tends toconcentrate in the blades 16 and 18, and the magnetic field density inthe blades 16 and 18 when they are closed is greater than when they areopen. Thus it is seen that the function of the magnet 24 is that of aholding magnet which, although the total magnetic field thereof does notchange, the effective field through the switch blades does change, beinggreater when the blades are closed and less when the blades are open.The two magnetic field intensities in the blades are such that once theblades are closed, the effective magnetic force therein tending to holdthem closed is greater than the spring bias tending to open them, andthe effective magnetic force tending to close these blades when they areopen is less than the spring bias serving to hold them apart. It is thischaracteristic which provides the bi-stable action of holding the bladesclosed once they are closed or leaving them open once they are opened.

The manner of opening and closing the blades may be performed by anytechnique desired. One suitable manner in which this might be performedis to use another magnet having a field which aids that of the fixedmagnet 24. The aiding magnet in conjunction with the fixed magnetsupplies a magnetic field to the blades which is lsufliciently strong topolarize the blades and effect a closing operation by magneticattnaction against the spring bias, and when the aiding magnet isremoved the magnetic field of the holding magnet is effective tomaintain lsufficient polarization to keep the contacts closed.- When 1tis desired to open the contacts, a further magnet poled to oppose themagnetic field of the holding magnet Z4 may be `brought into thevicinity thereof. The opposing fields thus provide an effective field onthe blades which s insuflicient to hold these blades closed against Ithesprlng bias inherent in the blade arms 16 and 18. Consequently, theblades separate and the switch is opened. Once the opposing magnet isremoved, the effective field from the holding magnet is insufficient toreclose the contacts 12 and 14, and hence the switch remains open.

The aiding and `opposing magnets may be the same magnet which is broughtinto the vicinity of the holding magnet 24, first in an aidingrelationship to close the contacts and second in an opposingrelationship to open the contacts. Alternatively, two separate magnetsmay be employed.

The eld strength of the aiding magnet in one arrangement may besufficiently strong to close the switch arms 16 and 158 without the aidof the holding magnet. In another arrangement the field strength of theaiding magnet may be insuflicient alone to polarize the switch arms andeiect a closure by magnetic attraction, but in combination with theiield strength of the holding magnet the two magnets provide a magneticheld intensity sufficient to polarize and close the switch arms bymagnetic attraction against the spring bias. The held strength of theopposing magnet must be suicient to eifectively cancel the eld of lcheholding magnet to the point where the elective magnetic held on theswitch arms is insuihcient to polarize these switch arms and hold themby magnetic attraction against the spring bias. The strength of theopposing magnet must of necessity be limited. If it is too strong, itserves to polarize the switch arms in the opposite direction andmaintain the switch arms closed against the spring bias by the reversepolarization. Thus it is seen that the aiding magnet may include anymagnetic iield strength above a given minimum. The opposing magnet musthave a iield strength sufciently large to electively balance out themagnetic field of the holding magnet at the switch arms, yet thestrength of the opposing magnetic iield must not exceed that of theholding magnet by an amount which causes reverse polarization of theswitch arms and maintains them closed against the spring bias.

Referring next to FIGS. 2 and 3, the switch in FIG. 1 is illustrated ina commutating arrangement which involves no wiping contacts. A pluralityof switches are arranged in a circular pattern within a cylindricaldrum. FIG. 2 shows a cross-sectional view through the right half of thedrum and IFIG. 3 illustrates in plan view a portion of the drum alongthe line 3-3 in FIG. 2. As more clearly shown in lFIG. 2 a plurality ofswitches are designated generally at 40, 42, `44, 46. These switches arepreferably of the type shown and described in FIG. l, but numerous otherleaf-type switches may be utilized. A spacer 48 separates the switches40 and 42 while a spacer 50 separates the switches 44 and 46. A magnet52 having a threaded end portion 5'4 is screwed into a threaded bore 56.'Ilhis magnet serves as a holding magnet, and as explained withreference to the switch in FIG. l, it is positioned within a criticalzone :by adjusting its position longitudinally with respect to theswitch 42. A magnet 58 having a threaded end portion 60 is screwed intoa threaded bore 62 and is moved to the right or left to insure properpositioning in a critical zone of the switch 46. 'Ilhe switches `42 and44 share a single magnet 64 which has a threaded end portion 66 thatengages a threaded bore 68. By adjusting the position of the magnet 64longitudinally with respect to the switches 42 and 44, this magnet maybe positioned in the critical zone of both switches.

Movable magnets 70 and 72 lare disposed on a rotatable shaft 74. Asshown more clearly in FIG. 2, the magnet 70 has a threaded end portion76 which engages a threaded bore 78 located in an arm 80 of a mountingdisk `82. In a similar fashion the movable magnet 72 has a threaded endportion -84 which screws into a threaded bore 86 located in the end ofan arm 88 attached to a mounting disk '90. Binding collars 92 and 94hold the mounting disk 90 in proper position for the magnet 72 to movebetween the two banks of switches positioned circumferentially aroundthe lower inside portion of the drum, one bank including the switch y44and the other bank including the switch 46. In a similar fashion,binding collars 96 and 98 engage the mounting disk 82, and this -unit isproperly positioned by a spacer 100 so that the rotating magnet 70 movesbetween two banks of switches located circumferentially around the upperinside portion of the drum, one bank including the switch 40 and theother bank including the switch 42.

As shown FIG. 3 there are two arms on each mounting disk X which carrymovable magnets. The mounting disk 82 carries the magnet 70 in the army80 and a magnet 102 in an arm 104. Both arms V80 and 104 are connectedto the mounting disk 82. 'Ihe mount-ing disk 90 has two arms 88 and 106connected thereto with each arm carrying respective magnets 72and 108therein. If the shaft 74 is rotated in the clockwise direction asindicated by the arrow in FIG. 3, the moving magnets 70 and 102 causethe upper two circular banks of switches to be sequentially operated,whereas the movable magnets 72 and 108 cause the lower two banks ofswitches to be operated. Two types of operation yare possible. Forexample, if the switches are normally open, they may be sequentiallyclosed by one associated moving magnet and a short period later beopened by the other associated moving magnet. Alternatively if theswitches are normally closed, they may be sequentially opened by oneassociated moving magnet and a short period later be closed by the otheryassociated moving magnet. Conversion from either type of operation tothe other type of operation is secured by reversing the poles of bothmovable magnets.

Assuming it is desired to sequentially close the various switches for ashort period but leave them normally opened, the magnets 70 and 72 arepoled to perform as closing magnets, and as such they are poled to aidthe iield of the associated iixed magnets 52, 58 and 64. Thus themagnets 102 and 108 serve as opening magnets, and as such they are poledto oppose the associated fixed magnets 52, 58 and A64. The fixed magnets52, 58 and 64 serve as holding magnets which insure that the switchcontacts remain in whatever position they are in until the associatedmovable magnets effect a change in the position of the switch arms. Whenthe movable magnet 70, for example, approaches the switch 40 in iFIG. 2,the contacts of this switch are closed because the magnetic eld of themagnet 70 aids the magnetic eld of the fixed magnet 52 at the blades ofthe switch 40. The iield i-ntensity of the magnet 70 may be suficientalone to close the switch blades. On the other hand it may be insuicientalone to close the switch blades, but when combined with the `iield ofthe magnet 52, the net field may be suicient to close the switch blades.In either case the magnetic eld is sufficient to polarize the switchblades and close the switch contacts against the inherent spring bias ofthe switch blades. As the movable magnet 70 moves away -from the switch40, the magnetic eld supplied by the lixed magnet 52 to the switchblades is sufficient to hold these blades together against an inherentspring bias. As the mov-able magnet 70 proceeds in a clockwise directionaround the inside of the drum, switches located in the bank of switchesthat includes the switch 40 are likewise closed along the way. Themovable magnet 102 follows the movable magnet 70 and is poled oppositeto both magnets 52 and 70. When the magnet 10-2 reaches the switch I40,the resulting magnetic field through the switch blades is reduced to apoint where the inherent spring bias of these blades exceeds the closingforce of the net magnetic iield. Consequently the switch blades open,thereby separating the blade contacts. W-hen the magnet 102 leaves theswitch 40, the field of the xed magnet 52 on the switch blades isinsuflicient to force these blades together, and thus the switch 40remains open until the movable magnet 70 returns in the next revolutionto the switch 40. As the mov-able magnet 102 proceeds in a clockwisedirection around the inside of the drum, -associated switches located inthe bank of switches 4that includes the switch 42 are likewise openedalong the way.

The movable magnets 70 and 102 operate in conjunction with the xedmagnet 64 to open and close switches located in the bank of switchesthat includes the switch 42, and the movable magnets 72 and 108 operatein conjunction with the iixed magnets 58 and 64 to open and close thetwo banks of switches which include respective switches 44 and 46.Although four banks of switches are shown in the commutating device ofFIGS. 2 and 3,

'7 it is to be understood that the number of banks of switches may beincreased or diminished as desired. In the simplest form of commutatingdevice only a single bank of switches may be employed. Thus it is seenthat the bank of switches which includes the switch 40` and the bank ofswitches which includes the switch 42 are sequentially operated to closefor a short period and remain open for a relatively longer period. Theperiod during which a switch remains closed may be increased ordiminished by respectively increasing or decreasing the angle betweenthe two arms 80 and 104. The period during which a switch is closed isdetermined by the time which the magnet 102 lags behind the magnet 70.The time which a switch is open is detenmined by the period of timewhich the magnet 70 follows behind the magnet 102. It follows that theperiod of closure is relatively shorter than the period when the switchis open. In a `similar fashion the movable magnets 72 and 108 controlthe lower banks of switches, switch `44 being located in one of thebanks and the switch 46 being located in the other bank.

Signals are induced in electrical circuits associated with closedswitches. If the switches 40 and 4 2in FIG. 2, for example, are closedby the magnet 70, signals are induced in the electrical circuitsassociated with these switches as the magnet 70 moves toward and awayfrom these closed switches. Likewise as the magnet 102 subsequentlyapproaches these switches, signals of opposite polarity `are inducedbecause the magnet 102 is oppositely poled with respect to the magnet70. The signals induced by the magnet 102 occur as this magnetapproaches the switches 40 and 42 and continues until these switches areopened. If the angle .between the arms 80 and 104 is made suicientlygreat a region intermediate the two arms may be secured which is free ofmagnetic lines of iiux from both the magnets 70 and 102. The size ofthis region free of any magnetic iield may be controlled by varying thestrength of the magnets 70 and 10-2 'as well as the angle between thearms 80 and 104. As the strength of the magnets is decreased, the sizeof this region increases, and as the angle of displacement of the arms80 and 104 is increased, this region is enlarged. Once the angle ofdisplacement between the yarms 80 and 104 is iixed and the strength ofthe magnets 70 and 102 is selected, the size of the region vbetween thetwo arms free of any magnetic iield is determined.

In order to illustrate how the commutating switch dcvice is operated topermit sampling of electrical outputs without interference `from inducedsignals, assume thaat the switches 40 and 42 are opened. When the magnet70 lapproaches the switches I40 and 42 and reaches a given position, theswitches are closed, as explained above. The magnetic iield from themagnet 70 applied to the switches 40 and 42 induces a signal Iin theseswitches and their associated circuits as soon as the switches areclosed. The amplitude of the induced signal is determined by the speedand the magnetic tield intensity from the magnet 70, the amplitude ofthe induced signal being greatest Awhen this magnet is immediately underthe switch 40 and over the switch 42. As the magnet 70 moves away fromthese switches, the amplitude of the induced signal decreases `andreaches a value of zero when the region of zero magnetic fieldapproaches and surrounds the switches. As long 'as the switches 40 and42 are engulfed in the region of zeromagnetic iield, no signal isinduced therein, and the period of time during which this region engulfsthe switches is determined by the speed of the moving arms 80 'and 104.rllhis period may be increased or decreased by correspondinglydecreasing or increasing the rotational speed of the arms S and 1014. Itis during the period when the region of zero magnetic field surroundsthe switches 40 and 42 that electrical devices associated therewith maybe sampled and electrical measurements made which are tree and clear ofany induced signal by the moving magnets 70 and 102. As the region ofzero magnetic iieldv leaves the switches 40 and 42, the magnetic iieldof the magnet 102 approaches and is applied to the switches 40 and 42.The intensity of the applied magnetic iield increases Yas the magnet 102approaches these closed switches, thereby inducing a signal whichcommences fat a zero level and builds up to a' maximum level when themagnet 102 approaches these switches suiiiciently close to open them asexplained afbove. Since measurements of the electrical output of thedevices under investigation is already completed, the latter inducedsignal is without consequence. In :a similar fashion each of theremaining switches associated with the magnets 70 and `102 are in turnclosed iirst by the field of the magnet 70, subsequently opened by themagnetic iield of the magnet 102 and during the interim both switchesundergo a period of zero magnetic field during which associatedelectrical devices may be sampled without interference from signalsinduced by the moving magnetic iields. The magnets 72 and 10S and theirassociated switches are oper- Iated in a llike manner to sequentiallyopen and close each switch once during each revolution of the arms 88and 106.

Thus a novel switch device is provided which is very reliable inoperation, simple and easy toA manufacture. The switch is well adaptedfor use in a commutating type switch device, and because wiping contactsIare eliminated, its useful life is extended and operating costs arereduced. It is to be understood that various modifications and numerousother arrangements are readily suggested to one skilled in the art.

What is claimed is:

l. A commutator switch device including a plurality of magnetic switcheseach mechanically biased to one of two positions, means for applying `afixed magnetic ield to said switches, first and second magnets displacedfrom one another and movably mounted to move past each of said magneticswitches, said first magnet serving to apply a magnetic field whichoperates each switch to a second position against the mechanical bias,said fixed magnetic lield serving to hold each magnetic switch in thesecond position when the magnetic iield of the first magnet is removed,said displacement between the rst and second magnets being sufficientlygreat to provide ya region therebetween which is substantially free ofany magnetic iield from either magnet, said second magnet having amagnetic lield poled opposite to that of the irst magnet and serving toreduce the net magnetic iield of each switch when applied theretowhereby each magnetic switch is returned to the one position by itsmechanical bias.

2. The apparatus of claim l wherein said iirst and second magnets aredisposed on two arms which rotate about a common axis and said magneticswitches are arranged about the common axis to come under the influenceof the tirst and second magnets once each revolution of the two arms.

3. A commutator switch device including a plurality of magnetic switcheseach mechanically biased to one of two positions, one magnet for eachmagnetic switch placed in a critical region for applying a holdingmagnetic iield to said switches, rst and second magnets displaced fromone another and movably mounted to move past each of said magneticswitches, said iirst magnet serving to apply a magnetic iield which aidsthe holding magnetic iield to operate each switch to a second positionagainst the mechanical bias, said holding magnetic field serving to holdeach magnetic switch in the second position when the magnetic field ofthe first magnet is removed, said displacement between the irst andsecond magnets being suiciently great to provide a region therebetweenwhich is substantially free of any magnetic field from either magnet,said second magnet having a magnetic field poled opposite to that of thetirst magnet and serving to oppose the holding magnetic iield to reducethe net magnetic field of each switch when applied thereto whereby eachmagnetic switch is returned to the one position by its mechanical bias.

4. A `commutator switch device comprising a plurality of switches eachincluding a pair of magnetizable switch arms spring biased to normallyoccupy an open position, first means for applying a lixed magnetic eldto the switch arms of each of said switches, said fixed magnetic fieldlocated with respect to the switches such that the magnetic eld appliedto said switches is sufficient to hold closed any switches which are inthe closed position but is insulicient to close any magnetic switcheswhich are in the open position, second means to apply to said switchesan aiding magnetic field having a polarization like that of the fixedmagnetic eld, third means to apply to said switches an opposing magneticield having a polarization reversed from that of the fixed magnetic eld,and fourth means for moving the second means and the third meanssuccessively past each of said switches.

5. Apparatus in accordance with claim 4 wherein the fourth means is arotatable member and the second means and the third means are magnets,each of the magnets being mounted on the rotatable member and displacedfrom each other whereby the magnets sequentially operate the pluralityof switches once during each revolution of the rotatable member.

References Cited in the le of this patent UNITED STATES PATENTS2,523,297 Hastings Sept. 26, 1950 2,550,605 Schenck Apr. 24, 19512,795,773 Perkins et al. June 11 ,1957 2,803,720 Mason Aug. 20, 1957-2,821,597 Germanton et a1 Jan. 28, 1958 2,872,597 Ormond Feb. 3, 19592,877,315 Oliver Mar. 10, 1959 2,902,558 Peek Sept. 1, 1959 2,902,564Fleck Sept. 1, 1959 2,912,678 Robinson et al. Nov. 10, 1959 2,922,994Kennedy Jan. 26, 1960

